Hitherto in color printing of letters and figures various methods have been known for printing desired areas or letters in different color from those of other areas or letters, such as a wire dot printing method utilizing plural color ink ribbons wherein one ribbon of a desired color is given an impact by a pin head to transfer the color ink to a recording sheet; and a thermal transfer printing method utilizing plural color ink donor sheets wherein a color ink donor sheet is interposed between a thermal head and a recording sheet for each color and the ink is thermally transferred to the recording sheet. In either printing method, however, there are disadvantages, that in a plurality of color ink ribbons or color ink donor sheets are needed, the printing operation is repeated for each color so that the printing speed is slow, and in addition, ink is not efficiently used when letters are printed since ink on whole areas of color ink ribbons or color ink donor sheets is not transferred.
Other methods there are known such as an ink jet method by using plural color inks and jetting ink drops through a nozzle for every color ink so as to avoid color mixing, and an electro-photographic method wherein a latent image is formed on a photoreceptor by exposing to a laser beam modulated with image signals or light which is ON/OFF-controlled with a liquid crystal shutter (LCS). However, the former involves difficulties in controlling size of the ink drops and preventing clogging in the nozzles and further it requires complicated means for jetting ink drops to desired positions accurately. In the latter, the operation of light exposure and development must be repeated for every color so that a plurality of developing means are needed for the plurality of colors, and in turn a device for carrying out the electro-photographic method becomes large and expensive, and this method is still not free from color-mixing problem.
There is a method of recording color images by directly exposing to laser beams a light-sensitive sheet having uniformly coated thereon two or more kinds of photocurable microcapsules having sensitivity to light of different wave length regions in which different color formers are encapsulated (as described in Japanese Patent Application No. 175,897/86). The light-sensitive sheet is scanned with light signals, in conformity with image information, emitted from a plurality of laser beams of different wave length to which the microcapsules are sensitive and color images are formed upon pressure development in the presence of a color developer. According to this method a color image can be obtained with ease. However, this method still has the disadvantage that three independent laser beam sources having wave lengths corresponding to the three primary colors (R, G, B) are used. For such laser beam sources, gas lasers are used such as He-Cd.sup.+ laser (.lambda.=441.6 nm), Ar.sup.+ laser (.lambda.=514.5 nm) and He-Ne laser (.lambda.=632.8 nm), but a large and expensive oscillator is needed for every gas laser as well as an audio-optical element (e.g., TeO.sub.2) for modulation of every laser, and moreover three drive circuits are needed. Thus, the resulting recording device becomes complicated. In addition, the laser beams for the three primary colors passed through optical lenses, such as a beam combining lens and an f.theta. lens tend to be out of focus due to chromatic aberrations of glass, resulting in a degraded image quality.